Anti-tracking high voltage insulating materials

ABSTRACT

Tracking is reduced in insulators comprising one or more polymers and an anti-tracking filler system comprising (a) a hydrate of alumina having a specific surface area of at least 2 m 2  /g measured by the BET method, and (b) a compound selected from the group consisting of oxides, mixed oxides and mixtures of oxides wherein said compound contains at least one element selected from the group consisting of transition series elements, lanthanide series elements and nontransuranic actinide series elements.

This is a continuation of then pending application Ser. No. 434,126, filed Jan. 17, 1974 (now abandoned) which in turn was a continuation-in-part of then pending application Ser. No. 81,558, filed Oct. 16, 1970 (now abandoned).

BACKGROUND OF THE INVENTION

This invention relates to high-voltage insulating materials.

While polymeric materials are widely used for insulating a wide variety of electrical apparatus, they are not suitable for high voltage applications in contaminated atmospheres where moisture or fog, together with salts, dust particles and ionic pollution causes leakage currents to flow across the surface of the insulation. This current causes a rise in temperature with consequent moisture evaporation and ultimately dry hand formation. The electrical stress across these dry bands often exceeds the breakdown stress of the air-insulation interface, so that discharge or spark scintillation takes place. The spark temperature is extremely high, often 2000° C. or higher, and the heat produced may be sufficient to cause degradation of the insulation surface with the ultimate formation of carbonaceous spots. These carbonaceous spots usually link up in dendritic fashion and the organic insulation fails by progressive creepage tracking.

Over the years many solutions to these problems have been proposed of which perhaps the most effective has been the incorporation of hydrated alumina, preferably the trihydrate, in fairly substantial quantities to for example butyl rubber, epoxy resins, especially of the cycloaliphatic type, and, more recently, to ethylene-propylene rubbers as illustrated in U.S. Pat. Nos. 2,997,526; 2,997,527; and 2,997,528.

There have been several suggested modes of operation for the hydrated alumina, but whatever the correct mechanism, it is found in practice that polymeric materials containing large proportions of alumina trihydrate are substantially protected against tracking and usually fail only by progressive surface erosion. The amount of alumina hydrate required to produce the anti-tracking effect is very high, however, and is usually in the region of 50-90% by weight of the entire insulation. Especially in the case of polymers that are shaped by molding or extrusion as well as in the field of heat-recoverable articles, the high filler content is undesirable because the high temperature used and/or the radiation employed in cross-linking cause loss of the hydrated water with accompanying development of porosity and the formation of voids leading ultimately to failure of the insulation.

SUMMARY OF THE INVENTION

The present invention provides an electrically insulating material which comprises one or more polymers and an anti-tracking filler system comprising, (a) a hydrate of alumina have a specific surface area of at least about 2 m² /g, and (b) a compound from the group consisting of oxides, mixed oxides and mixtures of oxides wherein said compound contains at least one element from the transition elements, the lanthanide series of the nontransuranic actinide series, as defined hereinafter. The resulting electrically insulating material has an initial tracking voltage of at least 2.5 kilovolts when tested according to ASTM-D 2303-68 liquid contaminant incline plane test, incorporated herein by reference.

By a "transition element" there is herein meant the elements of sub-groups IVa, Va, VIa, VIIa, and Group VIII of Mendeleef periodic table which are not also in the nontransuranic actinide series, e.g., titanium, zirconium, and hafnium, vanadium, niobium, and tantalum; chromium, molybdenum and tungsten; manganese, technetium, and rhenium; and iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum.

By "lanthanide series" there is herein meant the elements cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

By "nontransuranic actinide series" there is herein meant the elements thorium, protactinium, and uranium.

DESCRIPTION OF PREFERRED EMBODIMENTS

All references to "specific surface area" in this specification are to that measured by the Brunauer, Emmett and Teller (BET) nitrogen absorption method assuming the area covered by a nitrogen molecule to be 16.2 A². (The BET method is referred to, for example, in "The Physics and Chemistry of Surfaces" by N. K. Adam published by Dover, and in "Solid Surfaces and the Gas-Solid Interface", Advances in Chemistry Series Vol. 33)

The alumina hydrate is preferably the trihydrate, Al₂ O₃.3H₂ O, and preferably constitutes a major amount of the anti-tracking filler system.

It has surprisingly been found that the use of alumina hydrate of high surface area greatly enhances the properties of the insulating compositions of the present invention. It is preferable for the specific surface area of the alumina hydrate to be at least 3 m² /g and advantageously greater than 6 m² /g. Especially good results are obtained when the specific surface area lies in the range of from 8 to 20 m² /g. Lower surface areas will still yield acceptable results. However, the surface area should not be below about 2.0 m² /g to obtain the surprising improvement in insulating properties disclosed herein.

The hydrated alumina advantageously has a maximum particle size less than about 4 microns and preferably less than about 2 microns. Since the specific surface area of hydrated alumina is not directly dependent on particle size, it is understood that the invention is not limited to a particular particle size range.

The specific surface areas and particle size distributions of two forms of alumina trihydrate suitable for use in the present invention are given below.

    ______________________________________                                                         A     B                                                        ______________________________________                                         weight % less than                                                                               100     100                                                  2 microns                                                                      weight % less than                                                                               99.5    80                                                   1 micron                                                                       weight % less than                                                                               60      21                                                   0.5 micron                                                                     specific surface  12-15   6-8                                                  area m.sup.2 /g                                                                ______________________________________                                    

Types A and B are sold by the Aluminum Company of America as "Hydral 705" and "Hydral 710", respectively. It is to be noted that the above surface areas are those claimed by Alcoa. Actual surface areas for samples of A have been found to vary from 6 to 21 m² /g, averaging about 12 m² /g.

Hydral 705 gives generally good results when used in the anti-tracking systems of the present invention, especially when the surface area is 10 m² /g or higher.

Alumina hydrate of the desired specific surface area may be prepared by methods known per se, for example, by dissolving alumina in caustic soda and then reprecipitating it by bubbling carbon dioxide through the solution. According to the pH and the rate of bubbling, the necessary values of which can easily be determined by experiment, alumina hydrate of the desired specific surface area can be obtained.

Among oxides, mixed oxides and mixtures suitable as component (b) there may be mentioned, for example,

(i) Transition metal oxides, for example, TiO₂, V₂ O₅, Cr₂ O₃, Fe₂ O₃, NiO₂, Ni₃ O₄, Co₂ O₃, Co₃ O₄, MoO₃, WO₃, Nb₂ O₅, and mixtures thereof.

(ii) Lanthanide series oxides, for example, Pr₆ O₁₁, Yb₂ O₃, Ce₂ O₃, holmium oxide, erbium oxide, and mixtures thereof.

(iii) Nontransuranic actinide series oxides, for example, UO₃, ThO₂ and mixtures thereof.

(iv) Mixed oxides containing one or more transition metals, for example, nickel titanate, nickel molybdate and cobalt silicate.

(v) Any of the above oxides, mixed oxides or mixtures carried on an ahydrous alumina support, e.g., nickel cobalt molybdate on alumina and cobalt oxide on alumina CoO.Al₂ O₃ (blue cobalt aluminate).

(vi) Any of the above systems doped with small quantities of alkali metal or alkaline earth metal oxides, especially Li₂ O and K₂ O.

It is understood that the above listing is illustrative only, and is not intended to be a complete list of all the oxides which are operable in the invention.

The component (b), which is believed to react synergistically with the alumina hydrate in reducing tracking, may in some cases be used in quantities down to or below 0.5% by weight based on the total weight of the insulation material, but in general is preferably present in an amount in the range of from 2 to 10%, especially from 3 to 5%. Although amounts higher than 10% may be employed, little additional benefit to the tracking and erosion properties is gained thereby with most oxides. However, with some oxides of the invention e.g., ThO₂, the oxide is preferably present in quantities of about 15% or more by weight.

The particle size and surface area of component (b) are not so important as that of the alumina hydrate but the best results appear to be obtained with materials having a particle size less than 75 microns (BS 200 mesh, U.S. Sieve No. 200) and, for ease of dispersion during preparation of the insulating material, it is preferable to use materials having a particle size less than 45 microns (B.S. 350 mesh, U.S. Sieve No. 325).

Compounds of iron, cobalt and chromium are especially preferred as component (b). Particularly good results are obtained when Co₃ O₄ is used as component (b). Ferric oxide, cobaltic oxide and chromic oxide are also very useful.

It has also been found that a given weight of some combinations of two or more substances as component (b) is more effective than the same weight of only one of the substances, i.e. a synergistic effect between the substances is noted. An especially good component is a mixture of Fe₂ O₃ and Co₂ O₃. Insulating materials incorporating a given weight of this mixture show substantially less erosion on testing than materials incorporating an equal amount of either Fe₂ O₃ or Co₂ O₃ alone.

One of the problems of the previously proposed anti-tracking compositions in which alumina hydrate is used alone has been the difficulty of obtaining good U.V. stability. Normally, for maximum weather and U.V. protection it is common practice to incorporate small quantities of carbon blacks, usually the channel type. Alternatively, organic U.V. absorbers such as, for example, substituted benzophenones or benzotriazoles are employed which are far less effective than carbon black, although they have the advantage that a variety of colors are obtainable using normal pigments. In the case of polymeric insulating materials for outdoor use, a lifetime exposure running into decades, typically 25-30 years, is required. Some polymeric insulating-materials are not sufficiently U.V. stable to last this length of time and it is therefore necessary to incorporate channel blacks into them. The effect of these channel blacks, even in small concentrations of the order of 0.3% or less, has, however, been catastrophic on the previously proposed insulation materials in that tracking failures have rapidly occurred.

One of the surprising features of the present invention is that carbon black fillers can be incorporated into the insulation, in amounts up to about 3% by weight, without failure by progressive creepage tracking occurring such materials failing only by erosion. This is obviously a very important advantage particularly where the base polymers do not have good U.V. resistance.

In general, the anti-tracking filler system will constitute from 20-75% of the total weight of the insulating material. However, owing to the synergistic effect between component (b) and the alumina hydrate it is possible to reduce the proportion to below 20% in some cases without loss of anti-tracking properties. This is especially useful in the formation of heat-shrinkable articles from the materials when proportions of from 20 to 35% are preferred to avoid the development of porosity during manufacture and to maintain the necessary elongation, modulus and tensile strength above the crystalline melting point. If the material is to be used in non-heat-shrinkable applications then it is preferred to increase the proportion of alumina hydrate since this effectively reduces erosion rates and also lessens the overall cost of the insulation. The preferred proportion of anti-tracking filler system (a) plus (b) thus falls within the range of from 30 to 60% of the total weight of the insulation in these cases.

In general any polymer normally used for high voltage insulation may be used in this invention. Among polymeric materials into which the anti-tracking system may be incorporated there may be mentioned polyolefins and other olefin polymers, obtained from two or more monomers especially terpolymers, polyacrylates, silicone polymers and epoxides, especially cycloaliphatic epoxides. Among epoxide resins of the cycloaliphatic type there may especially be mentioned those sold commercially by CIBA (A.R.L.) limited under the names CY 185 and CY 183. Particularly suitable polymers include polyethylene, ethylene/ethyl acrylate copolymers, ethylene/vinyl acetate copolymers, ethylene/propylene copolymers, ethylene/propylene non-conjugated-diene terpolymers, chlorosulphonated polyethylene, polypropylene, polydimethyl siloxane, diemthyl siloxane/methyl vinyl siloxane copolymers, fluoro silicones, e.g. those derived from 3,3,3-trifluoropropyl siloxane, carborane siloxanes, e.g. "Dexsil" polymers made by Olin Mathieson, polybutyl acrylate butyl/ethyl acrylate copolymers, butyl acrylate/acrylonitrile copolymers, butyl acrylate/glycidyl methacrylate copolymers, polybutene, butyl rubbers, ionomeric polymers, e.g. "Surlyn" materials sold by DuPont, or mixtures of any two or more of the above.

The present invention also provides a composition suitable for processing into the insulating material of the invention.

The present invention furthermore provides an anti-tracking filler system suitable for use in the insulating materials and compositions of the invention.

The present invention also provides an electrical component especially a cable, insulated by the insulating material of the invention.

The present invention also provides a shaped article made from an insulating material of the invention. The material may be cross-linked and, if desired, the property of heat-recoverability may be imparted to the article.

Among the many uses for the insulating materials of the present invention there may especially be mentioned the production of heat-shrinkable tubing, heat-shrinkable sheds and heat-shrinkable 3-core udders for cable connection and termination, especially at high voltages of up to 33 KV and higher (vide "Heat-shrinkable plastics for termination and jointing of power and auxiliary cables" D. Q. Ash, Ir Bagdzinski and R. J. T. Clabburn PROC.IEE Vol. 117, No. 7, July 1970 pp 1365-1372). These and other shaped parts are especially useful in the termination of high voltage cables to overhead lines, to transformers and to switchgear, especially in outdoor environments.

The insulating material of the present invention may also in some cases advantageously be applied to, for example, a termination in situ by application of the basic composition in the form of a lacquer in a suitable solvent, for example, toluene, xylene or carbon tetrachloride. In some cases, especially when the polymer component is a silicone, the composition may itself be sufficiently fluid for in situ application which will harden on standing.

It will be appreciated that although the primary purpose of the anti-tracking filler is to prevent creeptracking as outlined above, the materials will also be effective in stabilizing the insulation under arcing conditions, i.e. in cases where a direct arc passes between two parts of an electrical apparatus forming a carbonaceous track along its line. This phenomenon is slightly different from creep-tracking where, for example conducting contaminate and/or surface irregularities cause a leakage current and a dendritic carbonaceous path develops on the surface of the insulation.

The insulating material and compositions of the present invention may, if desired, contain other fillers, for example, flame retardants, reinforcing fillers, pigments and mixtures thereof.

The anti-tracking system can be incorporated into polymer(s) by any of the commonly used techniques, for example, in a twin-roll mill at elevated temperatures. Similarly the resulting compositions can readily be processed into sheets of material or other shaped articles by any of the usual methods.

The following examples illustrate the invention, parts and percentages being by weight unless otherwise stated. The surface area of the alumina trihydrate is 16.0 m² /g unless otherwise indicated.

EXAMPLE 1

The following formulations were prepared by compounding on a twin-roll mill:

    ______________________________________                                         Sample No.         1     2     3   4   5   6   7                               ______________________________________                                         Dimethyl silicone elasto-                                                                         30    30    30  30  30  30  30                              mer (containing a small                                                        amount of methyl vinyl                                                         siloxane)                                                                      Low density polyethylene                                                                          30    30    30  30  30  30  30                              (MFI 3)                                                                        Ethylene ethyl acrylate                                                                           30    30    30  30  30  30  30                              copolymer (19% ethyl                                                           acrylate)                                                                      Alumina trihydrate 30    60    30  45  60  --  --                              (Hydral 705)                                                                   Agerite Resin D    2     2     2   2   2   2   2                               (polymerized trihydro-                                                         quinaline oxidant)                                                             sold by Vanderbilt                                                             Calcined ferric oxide                                                                             5     5     --  --  --  5   30                              Triallyl cyanurate 1     1     1   1   1   1   1                               2,5-dimethyl 2,5-di-t-                                                                            1     1     1   1   1   1   1                               butyl peroxy hexyne-3                                                          ______________________________________                                    

After thoroughly mixing all the ingredients in the order given, plaques 5×2×0.25 inches were pressed at 200° C. for 10 mins. The cross-linked plaques were then tested according to the ASTM D2303-68 liquid contaminant inclined plane test which measures the tracking and erosion resistance of insulating materials. The test method used was the initial tracking voltage test in which the voltage is raised by 0.25 KV every hour and was identical to the ASTM test except that the voltage supply was 50 HZ and no silver paint was used in conjunction with the stainless steel electrodes. The silver paint is not necessary and its absence has no effect on the test result. The samples were used for testing approximately 24 hours after preparation and were stored at room temperature and humidity. They were not soaked in contaminant prior to test. The contaminant which was ammonium chloride had a resistivity of 380 ohm. cm. and contained 0.02% Triton X100 as wetting agent.

The results of the tests are given in Table 1.

Comparison of the results of the tests on Samples 1 to 7 clearly shows that whereas Samples 6 and 7 containing ferric oxide but no alumina hydrate track rapidly, and Samples 3, 4 and 5 containing alumina hydrate but no ferric oxide track after a relatively short period, Samples 1 and 2 containing both alumina hydrate and ferric oxide in accordance with the present invention are non-tracking and fail only by erosion after 200 and 270 minutes on test, respectively.

The results of the tests on Samples 3, 4 and 5 illustrate that in the absence of ferric oxide as component (b), an increased proportion of alumina hydrate does not prevent tracking.

The results of the tests on Samples 6 and 7, similarly show that, in the absence of alumina hydrate, an increased proportion of ferric oxide does not prevent tracking.

The results of the tests on Samples 1 and 2 show clearly the synergistic anti-tracking effect of a combination of alumina hydrate and ferric oxide.

A further experiment was carried out on Sample 1 to evaluate the rate of erosion. In this experiment, the voltage was maintained constant at 2 KV, and the contaminant contained 1% sugar in addition to the ammonium chloride. After 24 hrs. exposure to the scintillation a very small depression about 0.050 in. deep had eroded away, showing the extremely good erosion resistance. By comparison, Sample 3 tracked, under the same conditions after 150 minutes.

                                      TABLE 1                                      __________________________________________________________________________     Sample No. 1       2    3    4     5     6     7                               __________________________________________________________________________     Start up voltage KV                                                                       3.0     3.0  3.0  3.0   3.0   3.0   3.0                             Final voltage KV                                                                          3.75    4.0  3.25 3.5   3.5   3.0   3.0                             Tracking voltage KV                                                                       non     non  3.25 3.5   --    3.0   --                                         tracking                                                                               tracking                                                    Time to track 2"                                                                          --      --   69   120   130   8     14                              (minutes from start                                                            of test)                                                                       Comments   Sample eroded                                                                          Sample                                                                              Narrow                                                                              Sample                                                                               Sample                                                                               Substan-                                                                             Substantially                              through at                                                                             eroded                                                                              tracks                                                                              tracks,                                                                              eroded                                                                               tially                                                                               immediate                                  base after                                                                             through                                                                             with but then                                                                             rapidly                                                                              immediate                                                                            tracking.                                  200 mins. on                                                                           at base                                                                             slight                                                                              tended to                                                                            with some                                                                            tracking.                                        test,   after                                                                               tendency                                                                            "clean up"                                                                           tracking                                                       270 mins.                                                                           to den-                                                                             leaving a                                                                            then                                                           on test.                                                                            dritic                                                                              large deep                                                                           "cleaned                                                            tracking                                                                            erosion                                                                              up", sub-                                                           noted.                                                                              crater in                                                                            sequently                                                                the sample.                                                                          tracking                                                                       again.                                      __________________________________________________________________________

EXAMPLE 2

Test samples containing the following formulations were prepared as described in Example 1.

    ______________________________________                                         Sample No.            8       9                                                ______________________________________                                         Dimethyl silicone elastomer                                                                          30      30                                               (as in Example 1)                                                              Low density polythene 30      30                                               (as in Example 1)                                                              Ethyleneethyl acrylate copolymer                                                                     30      30                                               (as in Example 1)                                                              Alumina trihydrate Hydral 705                                                                        30      30                                               Agerite Resin D (antioxidant)                                                                        2       2                                                Calcined ferric oxide 5       --                                               Kosmos BB (a conducting carbon                                                                       1       1                                                black)                                                                         Triallyl cyanurate    1       1                                                2,5-dimethyl-2,5-di-t-butyl-                                                                         1       1                                                peroxy hexyne-3                                                                ______________________________________                                    

The following results were obtained using the test method described in Example 1.

    ______________________________________                                         Sample No.     8           9                                                   ______________________________________                                         Start up voltage, kV                                                                          1.5         1.5                                                 Final voltage  3.75        2.0                                                 Tracking voltage                                                                              Non-tracking                                                                               2.0                                                 Comments.      Sample eroded                                                                              Sample tracked                                                     at bottom elec-                                                                            after 125                                                          trode after 576                                                                            minutes on test.                                                   minutes on test.                                                ______________________________________                                    

EXAMPLE 3

Samples containing the following formulations were prepared and tested as in Example 1.

All samples contained 30 parts dimethyl silicone elastomer, 30 parts low density polyethylene, 30 parts ethylene/ethyl acrylate copolymer, 30 parts alumina trihydrate (Type A), 2 parts Agerite Resin D, 1 part triallyl cyanurate and 1 part 2,5-dimethyl-2, 5-di-t-butyl peroxy hexyne-3.

In Addition, Samples 10-19 contained 5 parts of the following components, respectively:

    ______________________________________                                         Sample 10.     NiO.sub.2                                                       Sample 11.     Ni.sub.3 O.sub.4                                                Sample 12.     Co.sub.2 O.sub.3                                                Sample 13.     Co.sub.3 O.sub.4                                                Sample 14.     Cr.sub.2 O.sub.3                                                Sample 15.     V.sub.2 O.sub.5                                                 Sample 16.     TiO.sub.2 (surface area 250 m.sup.2 /g)                         Sample 17.     MoO.sub.3                                                       Sample 18.     WO.sub.3                                                        Sample 19.     Nb.sub.2 O.sub.5                                                Sample 20 additionally contained a mixture 5 parts                             Fe.sub.2 O.sub.3 and 5 parts Co.sub.2 O.sub.3.                                 ______________________________________                                    

The results of the tests are shown in TABLE 2. It will be seen that Samples 13, 14, 16 and 20 gave especially good results and that all the samples show substantially better anti-tracking properties than Samples 3, 4 and 5, which contained only alumina hydrate.

                                      TABLE 2                                      __________________________________________________________________________     Sample No. 10     11      12     13     14     15                              __________________________________________________________________________     Start up voltage KV                                                                       3.0    3.0     3.0    3.0    3.0    3.0                             Final voltage KV                                                                          3.5    3.75    4.0    5.25   4.25   3.25                            Tracking voltage KV                                                                       non-tracking                                                                          non-tracking                                                                           non-tracking                                                                          non-tracking                                                                          non-tracking                                                                          non-tracking                    Comments   Eroded Sample eroded                                                                          Eroded Substantially                                                                         Slow erosion                                                                          Sample eroded                              through at                                                                            slowly removed                                                                         through at                                                                            no erosion                                                                            failed by                                                                             through at                                 base after                                                                            from test owing                                                                        base after                                                                            even after                                                                            flaming after                                                                         base after                                 165 mins.                                                                             to flaming of                                                                          265 mins.                                                                             580 mins.                                                                             320 mins.                                                                             106 mins.                                         surface only                                                                   partly eroded.                                               __________________________________________________________________________             Sample No. 16     17     18     19      20                             __________________________________________________________________________             Start up voltage KV                                                                       3.0    3.0    3.0    3.0     3.0                                    Final voltage KV                                                                          5.25   3.75   3.75   3.25    5.0                                    Tracking voltage KV                                                                       non-tracking                                                                          3.75   non-tracking                                                                          non-tracking                                                                           non-tracking                           Comments   Sample failed                                                                         Sample failed                                                                         Sample ero-                                                                           Eroded through                                                                         Very slow                                         by surface                                                                            by small                                                                              ded through                                                                           at base after                                                                          erosion. Sam-                                     flaming after                                                                         track in mid-                                                                         at base                                                                               96 mins.                                                                               ple hardly                                        588 mins.                                                                             dle of speci-                                                                         after 200      marked when                                              men.   min.           test discon-                                                                   tinued at                                                                      529 mins.                      __________________________________________________________________________

EXAMPLE 4

Samples containing the following formulations were prepared and tested as described in Example 1.

The results are shown in Table 3.

    ______________________________________                                         Sample No.       21      22      23    24                                      ______________________________________                                         Ethylene ethyl acrylate                                                                         200     200     100   100                                     copolymer (as in Example 1)                                                    Ethylene-propylene-ethyli-                                                                      80      80      80    80                                      dene norbornene terpolymer                                                     Low density polythene                                                                           --      --      100   100                                     (as in Example 1)                                                              Alumina hydrate (Hydral 705)                                                                    110     110     110   110                                     Agerite Resin D  5       5       5     5                                       Triallyl cyanurate                                                                              3       3       3     3                                       2,5-di methyl 2,5-di tert.                                                                      2       2       2.5   2.5                                     butyl peroxy hexyne-5                                                          Ferric oxide     15      --      15    --                                      ______________________________________                                    

    __________________________________________________________________________     Sample No. 21     22   23       24                                             __________________________________________________________________________     Start up voltage KV                                                                       3.0    3.0  3.0      3.0                                            Final voltage KV                                                                          4.0    3.25 4.5      3.5                                            Tracking voltage KV                                                                       non-tracking                                                                          3.25  4.25    3.5                                            Comments   Sample re-                                                                            Tracked                                                                             Sample   Failed by                                                 moved at 248                                                                          at 76                                                                               failed by                                                                               tracking                                                  mins. due to                                                                          mins.                                                                               flaming. at 137 min.                                               distortion re-                                                                             Erosion and                                                        sulting from                                                                               several                                                            heat of spark                                                                              small tracks                                                                   present. 392 mins.                                      __________________________________________________________________________

These results show the improved anti-tracking effects obtained using a system of the present invention in two different types of polymeric insulation.

EXAMPLE 5

Samples containing the following formulations were prepared and tested as described in Example 1. The results are shown in Table 4.

    ______________________________________                                         Sample No.             25      26                                              ______________________________________                                         Low density polythene (as in Example 1)                                                               200     200                                             Ethylene ethyl acrylate copolymer                                                                     40      40                                              (as in Example 1)                                                              Alumina hydrate (Hydral 705)                                                                          100     100                                             Agerite Resin D        2       2                                               Trially cyanurate      2       2                                               2,5 di methyl-2,5-di-tert. butyl peroxy                                                               2.5     2.5                                             hexyne-3                                                                       Ferric oxide           15      --                                              ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         Sample No.   25             26                                                 ______________________________________                                         Start up Voltage kV                                                                         3.0            3.0                                                Final Voltage kV                                                                            5.75           5.0                                                Comments     Non-tracking. Sample                                                                          Flame failed                                                    removed after 704                                                                             with some                                                       mins. on test, show-                                                                          indication of                                                   ing only some erosion.                                                                        tracking.                                          ______________________________________                                    

These results show the improved effect obtained using ferric oxide as component (b) in another type of polymeric insulation.

EXAMPLE 6

Samples containing the following formulations were prepared and tested as described in Example 1, except that the ammonium chloride had a resistivity of 330 ohm cm. (thus making the test slightly more severe).

    ______________________________________                                         Sample No.     27     28     29   30   31   32                                 ______________________________________                                         Dimethyl silicone                                                                             30     30     30   30   30   30                                 elastomer (containing                                                          a small amount of                                                              methyl vinyl siloxane)                                                         Low density polyethylene                                                                      30     30     30   30   30   30                                 (MFI 3)                                                                        Ethylene ethyl acrylate                                                                       30     30     30   30   30   30                                 copolymer (19% ethyl.                                                          acrylate)                                                                      Alumina trihydrate                                                                            30     30     30   30   30   30                                 (Hydral 705)                                                                   Agerite Resin D                                                                               2      2      2    2    2    2                                  (antioxidant)                                                                  Calcined ferric oxide                                                                         0      1      4    5    71/2 10                                 Triallyl cyanurate                                                                            1      1      1    1    1    1                                  2,5 dimethyl 2,5 di tert.                                                                     1      1      1    1    1    1                                  butyl peroxy hexyne-3                                                          ______________________________________                                    

The results obtained were as follows:

    ______________________________________                                         Sample Number  27     28     29   30   31   32                                 ______________________________________                                         Starting voltage KV                                                                           1.5    1.5    1.5  1.5  1.5  1.5                                Finishing voltage                                                                             2.5    2.75   3.0  3.25 3.0  3.25                               Time to track 2"                                                                              240    --     --   --   --   --                                                min.                                                            ______________________________________                                    

Samples 28-32 prepared in accordance with the present invention, were non-tracking and failed only by erosion after 320, 384, 428, 395 and 420 minutes, respectively. These figures illustrate that, where component (b) is ferric oxide, increasing the proportion does not result in increased tracking protection and only has a small effect, if any, on the erosion of the materials. However, with other oxides disclosed as operative in the invention larger proportions of the oxide may be required to obtain the desired anti-tracking properties in the insulation.

EXAMPLE 7

Three further compositions containing cobalt silicate, cobalt aluminate, and brown iron oxide, respectively, as component (b) were prepared and tested as described in Example 1.

    ______________________________________                                                                    Pts.                                                ______________________________________                                         Dimethyl silicone elastomer (containing 0.2 mole %                                                          30                                                of methyl vinyl siloxane)                                                      Low Density polythene (MFI 3.0)                                                                             30                                                Ethylene ethyl acrylate copolymer (18% ethyl acrylate)                                                      30                                                Alumina trihydrate (surface area 6.3 m.sup.2 /g.)                                                           30                                                Agerite Resin D              2                                                 Component (b) as in Table    5                                                 Triallyl cyanurate           1                                                 2,5 dimethyl 2,5 di tert. butyl peroxy hexyne-3                                                             0.5                                               ______________________________________                                    

The starting voltage was 3 KV and the following results were obtained.

                  TABLE 5                                                          ______________________________________                                         Sample            Final Voltage                                                No.   Component (b)                                                                              KV         Comments                                          ______________________________________                                         33    Blue cobalt 5.5        Sample removed at                                       silicate               647 mins. no tracking                                   (about 32%             only slight erosion                                     cobalt)                                                                  34    Blue cobalt 5.25       Non-tracking, sample                                    aluminate              removed at 569 mins.                                    (32% cobalt)           deeply eroded                                     35    Brown iron  3.75       Sample eroded through                                   oxide (Ref 645T        at base after 180 mins.                                 ex Bayer)                                                                ______________________________________                                    

EXAMPLE 8

These experiments illustrate the importance of the surface area of the alumina hydrate. The following formulations were prepared as described in Example 1.

    ______________________________________                                                               Pts                                                      ______________________________________                                         Dimethyl silicone elastomer (containing                                                                30                                                     0.2 mole % of methyl vinyl siloxane)                                           Low density polythene (M.F.I. 2.0)                                                                     30                                                     Ethylene ethyl acrylate copolymer                                                                      30                                                     (18% ethyl acrylate)                                                           Alumina trihydrate (surface area                                                                       30                                                     as in Table 6)                                                                 Agerite Resin D         2                                                      Ferric oxide            5                                                      Triallyl cyanurate      2.0                                                    2,5 dimethyl 2,5 di tert butyl peroxy                                                                  0.5                                                    hexyne-3                                                                       ______________________________________                                    

Test samples were tested as described in Example 1 but at a constant voltage of 3 KV, so that the time to track or erode at this voltage was determined. The results are presented in Table 6.

                  TABLE 6                                                          ______________________________________                                               Surface area                                                             Sample                                                                               of hydrate                                                               No.   m.sup.2 /g   Comments                                                    ______________________________________                                         36    0.5          Tracked at 24 mins.                                         37    1.8          Tracked at 58 mins.                                         38    2.1          Sample eroded with some small                                                  tracks at 65 mins.                                          39    3.7          Sample eroded through at 181 mins.                          40    4.8          Sample eroded through at 166 mins.                          41    5.0          Sample eroded at 195 mins.                                  42    6.3          Sample eroded at 200 mins.                                  43    10.5         Sample eroded at 360 mins.                                  44    12.3         Sample removed at 494 mins.                                                    approximately 1/4 thickness left.                           45    16           Sample removed at 523 mins                                                     approximately 1/4 thickness left                                               intact                                                      ______________________________________                                    

The above results show quite clearly that hydrates having a surface area below about 2.0 m² /g do not prevent tracking, while, surprisingly, materials containing hydrates of about 2.0 m² /g or higher surface area fail by erosion only. Although the mechanism by which alumina hydrates with a surface area above about 2.0 m² /g combine synergistically with the disclosed metal oxides is unknown, Table 6 clearly discloses that where the surface area is about 2.0 m² /g or over the hydrates confer increasing resistance to erosion as their surface area increases.

The surface areas were measured by the BET technique on a Micromeritics Surface Area Analyzer Model 2200 after initially degassing the samples for 40 minutes at 150° C.

EXAMPLE 9

This Example illustrates compositions based on various other polymers.

The following formulations were prepared and tested as described in Example 1.

    ______________________________________                                         Sample No.     46*    47*    48   49   50   51                                 ______________________________________                                         Polyethylene (MFI 3.0)                                                                        --     --     100  100  --   --                                 Ethylene/propylene                                                                            --     --     --   --   100  100                                copolymer 30%                                                                  propylene)                                                                     Polydimethyl Siloxane                                                                         100    100    --   --   --   --                                 Aerosil 200 (Fine particle                                                                    30     30     --   --   --   --                                 size silica)                                                                   Alumina trihydrate (Sur-                                                                      30     30     20   20   50   50                                 face Area 6.3 m.sup.2 /g)                                                      Ferric Oxide   --     5      --   20   --   5                                  Triallyl cyanurate                                                                            2      2      2    2    2    2                                  2,5-dimethyl-2,5-                                                                             1      1      1    1    2.5  2.5                                ditertiarybutyperoxy-                                                          hexane-3                                                                       ______________________________________                                          *Substantially identical results were obtained using a copolymer of            dimethyl siloxane and 0.2 mole % methyl vinyl siloxane in place of pure        polydimethyl siloxane.                                                   

The following results were obtained:

                  TABLE 7                                                          ______________________________________                                         Sample No.                                                                             Starting Voltage                                                                            Final Voltage                                                                             Comments                                       ______________________________________                                         .sup. 46*                                                                              1.5 kV       2.25 kV    Complete failure                                                               by tracking                                    .sup. 47*                                                                              1.5 kV       2.75 kV    Failed by erosion                              48      1.5 kV       2.5 kV     Sample failed by                                                               several tracks                                                                 and flame failure                                                              after 243 minutes                              49      1.5 kV       2.75 kV    Sample failed by                                                               erosion after 310                                                              minutes                                        50      1.5 kV       2.5 kV     Sample failed by                                                               deep tracking                                                                  erosion and flame                                                              failure after 280                                                              minutes                                        51      1.5 kV       2.75 kV    Sample failed by                                                               erosion at 319                                                                 minutes                                        ______________________________________                                          *Substantially identical results were obtained using a copolymer of            dimethyl siloxane and 0.2 mole % methyl vinyl siloxane in place of pure        polydimethyl siloxane.                                                   

EXAMPLE 10

This example illustrates the use of oxides of the lanthanide and actinide series.

The following formulations were prepared and tested as in Example 1.

    ______________________________________                                                          52                                                            Sample No.       Comparison 53     54   55                                     ______________________________________                                         Dimethyl siloxane                                                                               30         30     30   30                                     elastomer (containing                                                          0.2 mole % methyl                                                              vinyl siloxane)                                                                Low density polythene                                                                           30         30     30   30                                     (MFI 3.0)                                                                      Ethylene/ethylacrylate                                                                          30         30     30   30                                     copolymer (as in                                                               Example 1)                                                                     Alumina trihydrate                                                                              30         30     30   30                                     (surface area 6.3 m.sup.2 /g.)                                                 Agerite Resin D  2          2      2    2                                      UO.sub.3 *       --         5      --   --                                     Pr.sub.6 O.sub.11 *                                                                             --         --     5    --                                     Ce.sub.2 O.sub.3 *                                                                              --         --     --   5                                      Triallyl cyanurate                                                                              1          1      1    1                                      2,5-dimethyl-2,5 0.5        0.5    0.5  0.5                                    di-t-butyl peroxy                                                              hexyne-3                                                                       ______________________________________                                          *Purities were 99.9+%                                                    

The ASTM test was commenced at 3.0 kV and the following results were obtained.

                  TABLE 8                                                          ______________________________________                                         Sample No.                                                                              Final Voltage                                                                             Comments                                                   ______________________________________                                         52       3.25 kV    Tracked at 69 minutes                                      Comparison                                                                     53       3.75 kV    Eroded and tracked at 183 minutes                          54       3.25 kV    Wide erosion sample tracked at                                                 89 minutes                                                 55       3.50 kV    Severe erosion and slight                                                      tracking after 160 minutes                                 ______________________________________                                    

The above figures show that, although in general the results obtained using these oxides are not so good as those obtained using transition metal oxides, there is a definite improvement in anti-tracking properties when compared to the use of alumina trihydrate alone.

EXAMPLE 11

This example illustrates the use of thorium oxide.

The formulations were prepared and tested as in Example 1, except that the ammonium chloride had a resistivity of 385 ohm cms., thus making the test slightly less severe.

    ______________________________________                                         Sample Number    56*   57*     58** 59**/60*                                   ______________________________________                                         I.C.I. Silicone Elastomer                                                                       30    30      30   30                                         E 322/60                                                                       L.D. polyethylene, MFI 3.0.                                                                     30    30      30   30                                         Ethylene-ethyl acrylate                                                                         30    30      30   30                                         copolymer (18% ethyl                                                           acrylate)                                                                      Alumina trihydrate                                                                              30    30      30   30                                         Thorium oxide, ThO.sub.2                                                                        20    60      10   --                                         Agerite Resin D   2     2       2    2                                         Triallyl cyanurate                                                                               1     1       1    1                                         2,5 dimethyl 2,5 di tert.                                                                        1     1       1    1                                         butyl peroxy hexyne-3                                                          ______________________________________                                          *Alumina trihydrate surface area was 11.1 m.sup.2 /g.                          **Alumina trihydrate surface area was 6.44 m.sup.2 /g.                   

The ASTM test was commenced at 2.5 KV, and the following results were obtained.

                  TABLE 9                                                          ______________________________________                                         Sample Number                                                                             56         57        58    59/60                                    ______________________________________                                         Start up voltage                                                                          2.5        2.5       2.5   2.5                                      KV                                                                             Final voltage KV                                                                          2.75       2.5       2.75  2.75                                     Tracking voltage                                                                          2.75       2.5       2.75  2.75                                     KV                                                                             Time to track 2"                                                                          101        28        70    72/75                                    (minutes from                                                                  start of test)                                                                 Comments:  Started to Tracking  Single                                                                               Tracking                                            track at 17                                                                               started   carbon                                                                               started                                             mins., but at 14 min.                                                                               track after                                               cleaned up,          formed                                                                               10 mins.                                            to fail by                                                                     eroded track.                                                       ______________________________________                                    

The test results in Table 9 demonstrate that thorium oxide performs according to the invention. Best results with thorium oxide are obtained by using alumina hydrate of a fairly high surface area and a moderate amount of the oxide. It is preferable to avoid use of the oxide in large quantities.

EXAMPLE 12

This example further illustrates the use of oxides and mixtures of oxides in the lanthanide series.

The following formulations were prepared and tested as in Example 1, except that the ammonium chloride had a resistivity of 385 ohm cms., thus, making the test slightly less severe.

    ______________________________________                                         Sample Number   61a    62a    63a  64a  65a  66                                ______________________________________                                         I.C.I. Silicone Elastomer                                                                      30     30     30   30   30   30                                E 322/60                                                                       L.D. Polyethylene, MFI 3.0                                                                     30     30     30   30   30   30                                Ethylene-ethyl acrylate co-                                                                    30     30     30   30   30   30                                polymer (18% ethyl                                                             acrylate)                                                                      Alumina trihydrate                                                                             30     30     30   30   30   30                                (surface area-10.2 m.sup.2 /g)                                                 Holmium oxide   --     5      --   --   --   --                                Praeseodymium oxide                                                                            --     --     5    --   --   --                                Pr.sub.6 O.sub.11.sup.1                                                        Ytterbium oxide.sup.1                                                                          --     --     --   5    --   --                                Erbium oxide.sup.1                                                                             --     --     --   --   5    --                                Cerium oxide.sup.2                                                                             --     --     --   --   --   5                                 Agerite Resin D 2      2      2    2    2    2                                 Triallyl cyanurate                                                                             1      1      1    1    1    1                                 2,5 di methyl 2,5 di tert.                                                                     1      1      1    1    1    1                                 butyl peroxy hexyne-3                                                          ______________________________________                                          .sup.1 Purities were 99.9+%                                                    .sup.2 Commercial grade sample of 50% cerium oxide with the remainder          being oxides of all other lanthanide elements.                           

Samples 61b-65b correspond to samples 61a-65a respectively and were prepared from the same components in the same amounts except that the alumina trihydrate had a surface area of 5.8 m² /g.

The ASTM test was commenced at 2.5 KV. The results are presented in Table 10.

                  TABLE 10                                                         ______________________________________                                                                 Time to                                                Sam-  Final    Tracking track 2"                                               ple   voltage, voltage, (mins. from                                            No.   KV       KV       start of test)                                                                          Comments                                      ______________________________________                                         61a   3.0      2.5      147      Tracking started                              (Com-                            at 20 mins. Sev-                              pari-                            eral tracks were                              son)                             evident by 120                                                                 mins. which later                                                              joined together                                                                producing final                                                                failure.                                      62a   3.5      3.25     270      Erosions started at                                                            82 mins. Later                                                                 large eroded crater                                                            formed, which pro-                                                             gressed to top                                                                 electrode with some                                                            tracking.                                     63a   3.5      3.25     294      Erosion started at                                                             13 mins. Large                                                                 eroded crater                                                                  formed and ulti-                                                               mate failure was                                                               by single carbon                                                               track from top of                                                              crater.                                       64a   3.5      3.5      253      Erosion started at                                                             55 mins. Large                                                                 eroded crater                                                                  formed and failure                                                             was by tracking                                                                with very large                                                                eroded crater at                                                               bottom electrode.                             65a   3.25     3.0      239      Erosion started at                                                             81 mins. Failure                                                               due to large                                                                   eroded crater with                                                             single track at                                                                top.                                          66    3.5      3.25     294      Erosion started                                                                at 33 mins. Fail-                                                              ure due to eroded                                                              crater with                                                                    single carbon                                                                  track at top.                                 61b   2.75     2.5       62      Tracking started                              (Com-                            after 10 mins.                                pari-                                                                          son)                                                                           62b   3.0      3.0      175      Initially some                                                                 erosion, but this                                                              turned to a                                                                    single carbon                                                                  track.                                        63b   3.0      3.0      176      Erosion started                                                                at 15 mins.                                                                    Later several                                                                  carbon tracks                                                                  started even-                                                                  tually going                                                                   up, causing fail-                                                              ure.                                          64b   3.0      3.0      147      Erosion initially                                                              but carbon tracks                                                              formed which                                                                   linked up to one                                                               single track.                                 65b   3.25     3.0      191      Failure due to                                                                 carbon tracks                                                                  after small                                                                    eroded crater                                                                  formed.                                       ______________________________________                                    

The test results in Table 10 demonstrate that the lanthanide oxides act synergistically, even at low surface areas, with alumina hydrate, giving increased resistance to tracking over alumina hydrate alone.

The test results in Table 10 may be advantageously compared with those presented in Example 8 to demonstrate that the surface area of the alumina trihydrate similarly affects the degree of anti-tracking resistance imparted to electrical insulators by all of the oxides and mixed oxides disclosed as operative in the invention. Thus, as shown in Example 8, with iron oxide, the time for erosion failure increases from 166 through 360 to 523 minutes as the surface area of the alumina hydrate is increased from 3.7 through 10.5 to 16 m² /g. Similarly, in the case of ytterbium, the time for erosive failure increases from 147 to 253 minutes as the surface area is increased from 5.8 to 10.2 m² /g.

In contrast, the effect of surface area variations in the alumina trihydrate when the latter is used alone appears to be minimal, as can be seen from the following Table drawn up from the comparative samples tested and reported elsewhere in this specification.

                  TABLE 10a                                                        ______________________________________                                                     Surface Area                                                       Sample      m.sup.2 /g Time to track 2"                                        ______________________________________                                         61b         5.8        62                                                      52          6.3        69                                                      59          6.44       72                                                      61a         10.2       147                                                     69          10.9       30                                                      60          11.1       75                                                      3           16         69                                                      ______________________________________                                    

Table 10a, allowing for two apparently anomalous results, indicates that, in the absence of an additional filler in accordance with the present invention, the anti-tracking properties are virtually independent of the surface area of the alumina trihydrate and, implicitly, indicates a synergistic relationship between such fillers and the said surface area.

EXAMPLE 13

This example compares the effectiveness of a composition employing a metal oxide within the scope of the invention (calcined ferric oxide) with that of a metal oxide outside the scope of the invention (zinc oxide).

The following formulations were prepared and tested as described in Example 1.

    ______________________________________                                         Sample No.         67      68      69                                          ______________________________________                                         ICI Silicone Elastomer                                                                            30      30      30                                          E 322/60                                                                       LD polyethylene, MFI 3.0                                                                          30      30      30                                          Ethylene-ethyl acrylate co-                                                                       30      30      30                                          polymer-18% ethyl acrylate                                                     Alumina trihydrate 30      30      30                                          (surface area 10.9 m.sup.2 /g)                                                 Agerite Resin D    2       2       2                                           Zinc Oxide         --      5       --                                          Calcined ferric oxide                                                                             5       --      --                                          Triallyl cyanurate 1       1       1                                           2,5 dimethyl 2,5 di tert.                                                                         1       1       1                                           butyl peroxy hexyne-3                                                          ______________________________________                                    

The results obtained are reported in Table 11 below.

                  TABLE 11                                                         ______________________________________                                         Sample No.                                                                               67          68          69                                           ______________________________________                                         Start up voltage                                                                         3.0         3.0         3.0                                          KV                                                                             Final voltage                                                                            3.25*       3.25        3.0                                          KV                                                                             Tracking volt-                                                                           non-tracking                                                                               3.25        3.0                                          age KV                                                                         Time to track         80          30                                           2" (minutes                                                                    from start of                                                                  test)                                                                          Comments: *Sample failed                                                                             Deep eroded Sample                                                 at 119 mins. by                                                                            track between                                                                              started                                                catching fire                                                                              electrodes. tracking                                               at edge of sam-                                                                            Tracking com-                                                                              immediately                                            ple. No track-                                                                             menced within                                                                              voltage ap-                                            ing occured.                                                                               10 mins. of plied.                                                             voltage appli-                                                                 cation.                                                  ______________________________________                                    

The above figures clearly show that the use of zinc oxide with alumina hydrate does not prevent tracking failure of the insulating material whereas the use of ferric oxide in the place of zinc oxide in an otherwise identical formulation completely eliminates tracking failure. Although sample 68, containing zinc oxide, took longer to fail by tracking than control sample 69, containing alumina hydrate alone, failure of sample 68 was still a tracking failure. This demonstrates that zinc oxide does not act synergistically with alumina trihydrate to give vastly improved resistance to tracking failure as do the oxides and mixed oxides of the invention.

EXAMPLE 14

This Example illustrates the use of the insulation materials of the present invention in heat-recoverable articles.

Using a formulation as specified in Example 1, Sample 1, a shed of internal diameter 0.49 inches was prepared by moulding at 190° C. for 12 minutes. After moulding, the shed was cooled in water, trimmed and then heated in a glycerine bath at 170° C. for 3 minutes. A PTFE mandrel of diameter 1.1 inches was then forced through the shed and then the mandrel plus shed was cooled in cold water for 5 minutes, whereupon the mandrel was removed. The shed then had an internal diameter of 1.05 inches. It was pore free. It was then reheated with a hot air gun to 170° C. whereupon it shrank and completely recovered to an internal diameter of 0.49 inches.

Similar results were obtained with a larger shed of internal diameter 1.05 inches which was expanded to 2.2 inches, and then completely recovered.

Using the same formulation, but with the peroxide absent, tubing of the following dimensions was prepared by extrusion.

    ______________________________________                                         Internal diameter                                                                              0.475 inches                                                   Wall thickness  0.095 inches                                                   ______________________________________                                    

The tubing was irradiated using a 1.5 mev electron beam to a total dose of 12 megarads. The tubing had the following properties.

    ______________________________________                                                       23° C.                                                                           150° C.                                          ______________________________________                                         Tensile Strength                                                                               101.3 Kg/cm.sup.2                                                                         15.3 Kg/cm.sup.2                                    Elongation at break                                                                            416%       293%                                                100% Modulus    --          6.8 Kg/cm.sup.2                                    ______________________________________                                    

This tubing was then expanded in a Raychem tubing expander of the type described and claimed in British Pat. No. 990,235 at a temperature of 140° C. The tubing obtained had an internal diameter of 1.10 inches. On heating, the tubing immediately recovered to its original internal diameter.

The tubing and sheds described above were successfully utilized to form a support insulator of the type described in British Pat. No. 1,292,276.

An epoxy polyamide/bisphenol A resin system was used as adhesive. 

I claim:
 1. Solid electrically insulating material suitable for high voltage applications which comprises one or more polymers suitable for electrical insulation use and from about 20% to about 75% by weight of an anti-tracking filler system comprising: (a) a hydrate of alumina having a specific surface area of at least about 2 m2/g, measured by the BET method, and (b) at least about 0.5% by weight of the total weight of the electrically insulating material of a compound selected from the group consisting of oxides, mixed oxides, and mixtures of oxides, wherein said compound contains at least one element selected from the group consisting of transition series elements, lanthanide series elements, and nontransuranic actinide series elements, said electrically insulating material having an initial tracking voltage of at least about 2.5 kilovolts when tested according to ASTM-D 2303-68 Liquid Contaminant Inclined Plane test.
 2. An electrically insulating material as claimed in claim 1 wherein said element is selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, and uranium.
 3. An electrically insulating material as claimed in claim 1, wherein the hydrate of alumina is the trihydrate, Al₂ O₃.3H₂ O.
 4. An electrically insulating material as claimed in claim 3, wherein the specific surface area of the alumina hydrate is at least 3 m² /g.
 5. An electrically insulating material as claimed in claim 4, wherein the specific surface area of the alumina hydrate is at least 6 m² /g.
 6. An electrically insulating material as claimed in claim 3, wherein the specific surface area of the alumina hydrate lies in the range of from about 8 to about 20 m² /g.
 7. An electrically insulating material as claimed in claim 4, wherein the maximum particle size of the alumina hydrate is less than about 4 microns.
 8. An electrically insulating material as claimed in claim 7, wherein the maximum particle size of the alumina hydrate is less than about 2 microns.
 9. An electrically insulating material as claimed in claim 1, wherein the alumina hydrate is alumina trihydrate having 100% by weight of its particles of a size less than 2 microns, 99.5% of size less than 1 micron, 60 of size less than 0.5 micron and a specific surface area substantially in the range of from about 12 to about 15 m² /g.
 10. An electrically insulating material as claimed in claim 1, wherein component (b) of the anti-tracking filler system contains a transition metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum.
 11. An electrically insulating material as claimed in claim 10, wherein the transition metal is selected from the group consisting of iron, cobalt and chromium.
 12. An electrically insulating material as claimed in claim 11, wherein component (b) is ferric oxide.
 13. An electrically insulating material as claimed in claim 11, wherein component (b) is chromic oxide.
 14. An electrically insulating material as claimed in claim 11, wherein component (b) is selected from the group consisting of Co₂ O₃ and Co₃ O₄.
 15. An electrically insulating material as claimed in claim 11, wherein component (b) is a mixture of ferric and cobaltic oxides.
 16. An electrically insulating material as claimed in claim 10, wherein component (b) is blue cobalt silicate.
 17. An electrically insulating material as claimed in claim 10, wherein component (b) is blue cobalt aluminate.
 18. An electrically insulating material as claimed in claim 1, wherein the anti-tracking filler system comprises from about 20 to about 35% of the total weight of the insulating material.
 19. An electrically insulating material as claimed in claim 1, wherein the anti-tracking filler system comprises from about 30 to about 60% of the total weight of the insulating material.
 20. An electrically insulating material as claimed in claim 1, wherein component (b) comprises from 2 to 10% by weight of the total weight of the electrically insulating material.
 21. An electrically insulating material as claimed in claim 1, wherein component (b) comprises from 3 to 5% by weight of the total weight of the electrically insulating material.
 22. An electrically insulating material as claimed in claim 1, wherein component (b) has a particle size less than 75 microns.
 23. An electrically insulating material as claimed in claim 22, wherein component (b) has a particle size less than 45 microns.
 24. An electrically insulating material as claimed in claim 1, wherein the polymer component is selected from the group consisting of polyethylene, an ethylene/ethylacrylate copolymer, an ethylene/vinyl acetate copolymer, an ethylene/propylene copolymer; an ethylene/propylene/non-conjugated-diene terpolymer, a chlorosulphonated polyethylene, polypropylene, polydimethyl siloxane, a dimethyl siloxane/methyl vinyl siloxane copolymer, a fluorosilicene, a carborane siloxane, polybutylacrylate, a butylacrylate/ethylacrylate copolymer, a butylacrylate/acrylonitrile copolymer, a butylacrylate/glycidyl methacrylate copolymer, polybutene, a butyl rubber, an ionomer and mixtures thereof.
 25. An electrically insulated material as claimed in claim 24, wherein the polymer component is a mixture of a dimethyl silicone elastomer, a low density polyethylene and an ethylene/ethyl acrylate copolymer.
 26. Electrically insulating material as claimed in claim 1 wherein the polymers have been cross-linked.
 27. A composition comprising one or more polymers, selected from the group consisting of organic and organometalic polymers a hydrate of alumina having a specific surface area of at least about 2 m² /g, measured by the BET method, and a compound selected from the group consisting of oxides, mixed oxides and mixtures of oxides, said compound containing at least one element selected from the group consisting of transition series elements, lanthanide series elements and actinide series elements, the total amount of said hydrate and said compound being between about 20% and 75% by weight of the composition, which composition is suitable for fabrication into a material as claimed in claim
 1. 28. An electrical component which is insulated by material as claimed in claim
 26. 29. An electrical component as claimed in claim 28, which is a high voltage cable.
 30. A shaped article which comprises insulating material as claimed in claim
 1. 31. A shaped article as claimed in claim 30, which is heat-recoverable.
 32. The insulating material of claim 1 further including up to about 3% by weight of carbon black.
 33. The material of claim 1 wherein said element is selected from the group consisting of titanium, vanadium, chromium, iron, cobalt, nickel, niobium, molybdenum, lanthanum, tungsten, cerium, praeseodymium, holmium, erbium, ytterbium, thorium and uranium.
 34. The electrically insulating material of claim 25 wherein the specific surface area of the hydrate of alumina is at least 4.0 m² /g. and at least one component of the group of oxides, mixed oxides and mixtures of oxides is selected from the group consisting of ferric oxide, chromium oxide, cobaltic oxide, cobaltic aluminate, titanium dioxide, and cobaltous oxide.
 35. The electrically insulating material of claim 34 wherein the anti-tracking filler system comprises from about 20 to about 35% of the total weight of the insulating material.
 36. An electrically insulating material as claimed in claim 1 wherein the polymer component is selected from the group consisting of, dimethyl silicone, polyethylene, ethylene ethyl acrylate, ethylene propylene-ethylidene norbornene terpolymer, polyethylene and ethylene ethyl acrylate copolymer, ethylene-propylene copolymer, polydimethyl siloxane, dimethylsilicone, methyl vinyl siloxane, dimethyl siloxane, methyl vinyl siloxane copolymers and mixtures thereof.
 37. The electrically insulating material of claim 36 wherein at least one component of the oxides, mixed oxides and mixtures of oxides is selected from the group consisting of oxides of iron, nickle, cobalt, chromium, vanodium, titanium, molybdonum, tungstun, mobium, uranium, praseodymium, cerium, thorium, holmium, yherbium, and erbium.
 38. An electrically insulating material as claimed in claim 37, wherein the polymer component is a mixture of a dimethyl silicone elastomer, polyethylene and an ethylene/ethyl acrylate copolymer.
 39. An electrically insulating material as claimed in claim 38 wherein at least one component of the oxides, mixed oxides, and mixtures of oxides is selected from the group consisting of oxides of iron, nickel, cobalt, chromium, vanodium, titanium, molybdonum, tungstun, mobium, uranium, phraseodymium, cerium, thorium, holmium, yherbium, and erbium.
 40. The electrically insulating material of claim 1 wherein the polymer is selected from the group consisting of a thermoplastic polymer and elastomeric polymer. 